Shoreline change of Chongming Dongtan and response to river sediment load: A remote sensing assessment

Chongming Dongtan, located in the center of the Yangtze estuary, is a Ramsar Wetland of International Importance and National Nature Reserve. The dramatic decrease in river sediment load has attracted considerable scientific interest to this area, but few studies have paid attention to the shoreline dynamics. This study uses Landsat images spanning from 1987 to 2010 and an orthogonal transect method, which was previously developed by the authors, to model the spatial and temporal characteristics of shoreline change and explore its relationship to reduced river sediment load by use of regression analysis on three different spatial scales. Results show a general decrease in the average rates of shoreline change throughout the entire study period. The maximum average shoreline change rate of +115.5m/year occurred in the 1987–1990 interval and the minimum rate of +20.4m/year occurred from 2006 to 2008. Based on average rates of shoreline change, the coast of Dongtan was divided into three segments: the erosion segment, eastern accretion segment, and northern accretion segment. The temporal pattern of the northern accretion segment is almost completely opposite to that of the eastern accretion segment. The strongest-correlation transects are located on the northern side of the eastern tip of Dongtan and the next strongest transects are located on the south side. Other transects have a very low correlation. Transect 19 near the easternmost tip of Dongtan has a near zero correlation (r2=0.0045) but has the fastest accretion rate, and in general an increase in the shoreline change rate. The average rate of shoreline change and the net accretion area in Dongtan as a whole are significantly associated with sediment discharge at Datong Station (r2=0.69 and 0.75, respectively). This implies that shoreline accretion in Dongtan will probably slow down gradually, if the river sediment load continues to decrease in the future. The shoreline change rates achieved using our approach are consistent with previous studies, but the relationship with the river sediment load is different from results in a previous study on intertidal wetland based on bathymetric maps. The results and methods may be helpful in coastal management and understanding the evolution of the entire delta from the perspective of shoreline change.